Suggestions for controlling the domestication of tilapia improved strains are given regarding: 1) the population that serves as foundation stock; 2) the breeding system employed; and 3) the process used for selecting brooding stock.
Bangladesh enters into international shrimp market in early 1970s but now it takes second places in the source of foreign currency earning. Now this sector facing a serious problem with a disease named White Spot Syndrome Virus which causes 100% mortality in the shrimp farm within two weeks. In Bangladesh, outbreak of White Spot Syndrome Virus has been a serious problem since 1995. In the present study, it was observed the present situation of White Spot Syndrome Virus prevalence in wild tiger shrimp brood, nauplii and post-larvae in Bangladesh.
The article is based on an ongoing collaboration in Vietnam between the WorldFish Center (formerly ICLARM) and the Ministry of Fisheries, at the Research Institute for Aquaculture No. 3, Nha Trang City, Khanh Hoa Province. The work described is oriented towards regions near the equator, where induced spawning of on-grown broodstock should be possible over about 10 months of the year. A shorter breeding season (in subtropical areas) would necessitate bigger installations, but a larger market size would have the opposite effect.
The controlled breeding of finfish for culture is reviewed with special refer-ence to recent developments and persistent problems. Freshwater species are at present cultured on a much larger scale than brackishwater and marine species which have potential for aquaculture in arid and semi-arid lands. A reliable supply of fish seed for freshwater farming can usually be produced from captive broodstock whereas coastal aquaculture still depends largely on collection of seed from the wild.
The freshwater river systems and floodplains of Bangladesh are the breeding grounds for 13 endemic species of carps and barbs and a large number of other fish species, including a number of exotic carps and other species that have been introduced for aquaculture. Since 1967, breeding of endemic and exotic aquaculture species for seed producton through hypophysation techniques has become a common practice.
Based on the encouraging results obtained by earlier workers, the concept for a floating hatchery was developed for producing tilapia for both farming and enhanced fisheries in the freshwater lakes and coastal lagoons of Gabon. The research and development work to test this concept was undertaken with Nile tilapia (Oreochromis niloticus). Two places in Gabon were selected, representing climatic and environmental condition similar to other parts of the country.
Between May and October 1990, fecundity, egg size and condition factor of Chrysichthys nigrodigitatus (Lacépède) in the Cross River, Nigeria, were studied. The fecundity (F) of this population varied from 3 046 eggs (total length, L=28.5 cm) to 28 086 eggs (L=64 cm). A mean relative fecundity of 231 eggs/cm or 13 eggs/g of fish was obtained for this population. The fecundity of this population can be estimated with the formula F=2.511 · L 2.30 or F=52.893 · W 0.78 , total length being in cm and weight (W) in g. The mean egg diameter of this population varied from 0.65 mm to 3.54 mm.
Following a survey of the important traits of Indian carp broodstock at some southern Indian hatcheries, it was found that the broodstock selection was size selective, exerting strong, negative selection of prematuration growth rate and positive selection on age at first maturation. This meant that the hatchery bred inadvertently slower growing and later maturing individuals. Details are given of approaches to avoid such negative selection and minimize inbreeding.
The reproductive potential of three tilapias (Oreochromis aureus, O. spilurus and a red tilapia from Taiwan) were tested in 2 m3 fiberglass tanks with a water salinity of 3-5 ppt. Also, the hybridization of O. spilurus and O. aureus was attempted. The tests lasted for 192-207 days. Eggs were collected weekly and incubated artificially. The number of fry produced was noted. Results showed O. spilurus to have the highest reproductive potential based on fry production (75 fry/m2/day) adn the longest spawning season.
The background to the setting up of the project is summarized and an outline of the project given. The 4 tilapiaspecies currently available are Sarotherodon mossambicus, S. niloticus, S. aureus and Tilapia zillii . The progress made so far is described briefly.